Find the 20th term from the last in the sequence 3,7,11.... 407 ?

• Reverse the Series 407,403,----,3
  Now using formula Tn = a + (n-1)d
  a=407
  d=-4
  n=20
  after solving T20 = 407+(20-1)(-4) = 331
• 12 years agoHelpfull: Yes(62) No(3)
• 331.
  
  Series is increased by 4.
  Want to find the 20th term from last means,
  we want to decrease by 4 from the last to 20the term from last.
  
  407 is last number in the sequence.
  therefore,
  407,403,399,395,391,387,383,379,375,371,367,363,359,355,351,347,343,339,335,(331)
• 13 years agoHelpfull: Yes(11) No(3)
• since in A.P. last term is 407 nd first is 3,
  a=3 l=407 nd d=4
  now l=a+(n-1)d,
  407=3+(n-1)4,
  n=102 then 20 from last is eqaul to 83 from start
  T83=3+(83-1)*4=331....
  
• 12 years agoHelpfull: Yes(5) No(0)
• 331 is the answer.
• 13 years agoHelpfull: Yes(4) No(1)
• Difference of 7,3 is 4.
  reverse the series as we need 20th number from last.
  therefore, 407,403,.....11,7,3
  now use the formula Tn=a+(n-1)d
  a=407
  d=-4(as we are have reversed the series)
  n=20(as we need 20th term from 407)
  Tn=407+(20-1)(-4)=> 407+19*-4 => 407-76 => 331(Ans)
  
• 12 years agoHelpfull: Yes(0) No(2)
• Total number of terms in AP :
  407=3+(n-1)4
  n=102
  Now 20th term from the last of the series will become's 83th term from the beginning of the series as (102-20+1=83)
  
  Now simply calculate the value of 83 term ;
  T=3+(83-1)*4 = 331
  
• 8 years agoHelpfull: Yes(0) No(1)